diff --git a/docker/auth/auth.py b/docker/auth/auth.py
index 1c29615546..d7fbd6b83f 100644
--- a/docker/auth/auth.py
+++ b/docker/auth/auth.py
@@ -102,12 +102,6 @@ def encode_header(auth):
     return base64.b64encode(auth_json)
 
 
-def encode_full_header(auth):
-    """ Returns the given auth block encoded for the X-Registry-Config header.
-    """
-    return encode_header({'configs': auth})
-
-
 def parse_auth(entries):
     """
     Parses authentication entries
diff --git a/docker/client.py b/docker/client.py
index e52cb53829..ce4a657139 100644
--- a/docker/client.py
+++ b/docker/client.py
@@ -139,7 +139,7 @@ def build(self, path=None, tag=None, quiet=False, fileobj=None,
             if self._auth_configs:
                 if headers is None:
                     headers = {}
-                headers['X-Registry-Config'] = auth.encode_full_header(
+                headers['X-Registry-Config'] = auth.encode_header(
                     self._auth_configs
                 )